This invention pertains to internal combustion engines and, more specifically, to preheaters for diesel fuel.
Particulate reduction in diesel fuel combustion can be effected by diesel fuel preheating to either a hot liquid or possibly a vapor state. Within the scope of this invention several ways have been conceived to provide a sufficient quantity of heat to the fuel to reduce its surface tension, viscosity and density to a minimum to improve the prechamber vaporization and burning ability. These include: electrical heating, low fuel pressure heating with the exhaust gas or water jacket, high fuel pressure discharge line heating with exhaust gas or water jacket, and/or injector element fuel heating with precombustor gas or water surrounding the injector. All of the above concepts can be made to work since the required heat input would be less than 0.94 Btu/sec for a 180.degree. F. diesel fuel temperature discharge.
The benefit of increasing the fuel temperature for improving the combustion efficiency of the diesel precombustor can be projected by observing the comparative smokiness in the diesel from starting cold to warm conditions. This is due to warming of the fuel delivery system and the precombustor wall elements. As shown in Table I, the fluid viscosity is markedly decreased from 60.degree. F. to 180.degree. F. As would be expected, the surface tension would also be reduced at higher temperatures. Both of these factors would appear to be contributory to a more rapid complete combustion in the prechamber and main chamber due to droplet size reduction effects and also a reduced vaporization time in the precombustor.
TABLE I __________________________________________________________________________ EFFECTS OF TEMPERATURE ON LIGHT OIL PROPERTIES t w c.sub.y.sup.a k.sup.a .mu..sup.a X.sup.b Y.sup.c .beta. .degree.F. lb/ft.sup.2 Btu/lb F Btu/ft hr F lb/hr ft N.sub.Pr N.sub.Pr.spsb.1/2 sec/ft.sup.2 1/ft.sup.3 F 1/.degree.F. __________________________________________________________________________ Water (saturated liquid) __________________________________________________________________________ 50 62.4 1.00 0.334 3.17 9.50 2.12 71,000 10 .times. 10.sup.6 0.06 .times. 10.sup.-2 60 62.4 1.00 0.339 2.71 8.00 2.00 82,800 22 0.10 70 62.4 1.00 0.344 2.36 6.86 1.90 95,000 35 0.12 100 62.0 1.00 0.358 1.66 4.64 1.67 134,700 129 0.22 150 61.2 1.00 0.382 1.04 2.66 1.38 212,000 445 0.31 200 60.1 1.01 0.406 0.738 1.83 1.22 294,000 1.08 .times. 10.sup.9 0.39 250 58.9 1.02 0.430 0.555 1.32 1.10 382,000 2.35 0.50 300 57.4 1.03 0.454 0.448 1.02 1.00 462,000 3.90 0.57 400 53.6 1.08 0.382 0.327 0.93 0.98 590,000 8.40 0.75 500 49.0 1.18 0.353 0.261 0.87 0.95 676,000 17.4 1.18 537 47.0 1.24 0.335 0.246 0.91 0.97 688,000 22.4 1.47 572 44.6 1.37 0.312 0.233 1.02 1.00 689,000 30 1.96 __________________________________________________________________________ Light Oil __________________________________________________________________________ 50 57.8 0.43 0.0770 315 1700 12.0 663 5.5 .times. 10.sup.3 0.39 .times. 10.sup.-2 60 57.6 0.43 0.0768 210 1180 10.5 987 12.2 0.39 70 57.4 0.44 0.0766 140 805 9.3 1475 27.4 0.39 100 56.6 0.45 0.0763 55 324 6.8 3710 178 0.40 150 55.4 0.48 0.0756 19 121 5.0 10,500 1.15 .times. 10.sup.6 0.41 200 54.2 0.50 0.0749 9 60 3.9 21,700 6.54 0.43 250 53.0 0.52 0.0743 5 35 3.3 38,200 20.6 0.44 300 51.8 0.54 0.0736 3 22 2.8 62,300 56.5 0.45 __________________________________________________________________________ .sup.a Substantially independent of pressure for p &lt; 20 atm. .sup.b N.sub.R.degree. = upx/.mu. = X for u = 1 ft/sec and x = 1 ft. .sup.c N.sub.Gr = (.beta.g.rho..sup.2 /.mu..sup.2)d.sup.3 .DELTA.t = Y fo d = 1 ft and .DELTA.t = 1 F.
Of the basic heating approaches incorporated in this invention, the use of a heat exchanger to cause either warming or "vaporization" downstream of the fuel pump would appear the best. Although workable, warming upstream of the fuel pump might sporadically effect the pump delivery rate. Warming of the diesel fuel after pumping to high pressure has the disadvantage of the high pressure heat exchange elements, but conversely will not affect the pumping and intake feed conditions.
The use of the engine jacket discharge water prior to radiator conditioning would appear to provide a clean, hot carbon-free temperature source if fuel temperatures up to 180.degree. F. would be sufficient. For higher temperatures, the use of added heating by the exhaust system (to 1000.degree. F.) can be envisioned.